Solar Power Batteries

In stand-alone systems, the power generated by the solar panels is usually used to charge a lead-acid battery. Other types of battery such as nickel-cadmium batteries may be used, but the advantages of the lead-acid battery ensure that it is still the most popular choice. A battery is composed of individual cells; each cell in a lead-acid battery produces a voltage of about 2 Volts DC, so a 12 Volt battery needs 6 cells. The capacity of a battery is measured in Ampere-hours or Amp-hours (Ah).

Battery Types

The number of times a battery can be discharged is known as its cycle life, and this is what determines its suitability for use with solar cells. Car batteries are the most common type of lead-acid battery, but will survive only 5 or 10 cycles so are unsuitable for our purposes. For solar applications a battery needs to be capable of being discharged hundreds or even thousands of times. This type of battery is known as a deep-cycle battery, and some of the many different types are explained here.

Leisure Batteries

Leisure batteries or caravan batteries are usually the cheapest type of deep-cycle battery. They look similar to a car battery but have a different plate construction. Their capacity is normally in the range of 60 to 120 Ah at 12 Volts, making them most suitable for smaller systems. The cycle life of leisure batteries is limited to a few hundred cycles, meaning that they are most suitable for systems which will not be used every day, such as those in caravans or holiday homes.

Traction Batteries

The term traction battery relates to all batteries used to power electric vehicles. This can mean anything from a mobility scooter to a fork-lift truck, so encompasses capacities from 30 or 40 Ah to many hundreds. The smaller traction batteries are usually 6 or 12 Volt units, where the largest are single 2 Volt cells. Traction batteries are ideal for solar power applications, as they are intended to be fully discharged and recharged daily. The larger traction batteries can withstand thousands of discharge cycles. There are also batteries known as semi-traction batteries, which can be thought of as higher quality leisure batteries, exhibiting a greater cycle life. Marine batteries also fall into this category.

Sealed Batteries

There are many types of sealed lead-acid batteries, ranging from those of 1 or 2 Ah to single cell traction batteries of hundreds of Amp-hours. The advantages of sealed batteries are obvious; they need no maintenance and are spill-proof. They do have disadvantages however; they are more expensive than other battery types, they require more accurate charging control and can have a shorter life, especially at high temperatures. Sealed batteries are most appropriate where the solar power system will need to operate for long periods without maintenance.